ELFT HÍRADÓ

[tcsaba <tcsaba AT eik.bme.hu>]

                   M E G H Í V Ó - I N V I T A T I O N

    Seminar Series of the Department of Theoretical Physics at the
           Budapest University of Technology and Economics


                            Jed H. Pixley
                      (University of Maryland)

    Rare region induced avoided quantum criticality in disordered
             three-dimensional Dirac and Weyl semi-metals


We study the effects of short-range random potential disorder on 
three-dimensional Dirac and Weyl semi-metals [1]. We focus on the 
proposed quantum critical point (QCP) separating a semi-metal and 
diffusive metal phase driven by disorder. We will briefly review the 
existing evidence of such a QCP [2] and the effects of large disorder 
[3]. We will then explore the non-perturbative effects of rare regions 
using Lanczos and the kernel polynomial method, from which we establish 
the existence of two distinct types of excitations in the weak disorder 
regime. The first are perturbatively renormalized dispersive Dirac 
states and the second are weakly dispersive quasi-localized “rare” 
eigenstates. We establish that these rare eigenstates contribute an 
exponentially small but non-zero density of states at zero energy, thus 
converting the semi-metal to diffusive metal transition into an avoided 
quantum critical point. Nonetheless, we show a quantum critical scaling 
regime still exists albeit only at finite temperature or energy. Lastly, 
we establish how to find the location of the avoided QCP and tune how 
strongly it is avoided.

[1] J. H. Pixley, David A. Huse, S. Das Sarma, arXiv:1602.02742 (2016).
[2] J. H. Pixley, Pallab Goswami, S. Das Sarma, Phys. Rev. B 93, 085103 
(2016).
[3] J. H. Pixley, Pallab Goswami, S. Das Sarma, Phys. Rev. Lett. 115, 
076601 (2015).

Időpont: 2016. június 3. péntek, 10:15
Helyszín: BME Fizikai Intézet, Elméleti Fizika Tanszék,
Budafoki út 8. F-épület, III lépcsőház, szemináriumi szoba